Pharmacokinetics of the novel anticonvulsant HEPP after single intravenous administration of three different doses in dogs

Gestational Age Dependency in the Prenatal Toxicity and in the Disposition Kinetics of the Novel Anticonvulsant HEPP (D,L-3-Hydroxy-3-ethyl-3-phenylpropionamide) after Subcutaneous Administration in Pregnant Rats

HEPP (D,L-3-hydroxy-3-ethyl-3-phenylpropionamide) is a novel anticonvulsant with promising anticonvulsant profile, which is being actively researched. The potential maternal and embryo/fetal toxicities of HEPP were evaluated in pregnant rats following subcutaneous (s.c.) administration during organogenesis (gestation days 6 through 14, GDs 6–14) and the fetal period (GDs 14–21). Single- and multiple-dose pharmacokinetics were also evaluated at the same periods in order to establish possible correlations with some maternal or embryo/fetal toxicity end points. Embryotoxicity was mainly indicated by a significant dose-concentration dependency in the increase in resorptions, high percentage of fully resorbed litters, and decrease in embryo body weights during the GD6–14 dosing period. No gross external alterations were observed in live fetuses. There was no indication of maternal toxicity; but a marked increase in maternal body weight was evident following dosing from GD14 to GD21. The maternal plasma profile following single subcutaneous dose of 50 mg/kg on both GD14 and GD21 showed a monoexponential elimination pattern. Statistically significant differences between treatments (GD14 versus GD21) were observed in elimination ( kel = 0.12 versus 0.15 h−1), absorption ( ka = 2.01 versus 3.14 h−1), maximum plasma concentration time points ( Tmax = 1.49 versus 1.01 h); maximum plasma concentration ( Cmax = 40.23 versus 36.31 μg/ml) and areas under the concentration-time curve (AUCs0– ∞ = 421.88 versus 274 μg h/ml. Based on comparisons of Cmax, Tmax, and AUCs0– ∞ between the actual data and single intraperitoneal (i.p.) data previously published, the s.c. administration exhibited slower disposition and higher absorbed amount. After multiple-dose administrations of 50 and 100 mg/kg every 12 h (07:00 and 19:00 h), steady-state plasma levels were lower than the computer prediction, and only slight accumulation was observed. In both dosing periods HEPP levels were similar in mothers and offspring at steady-state conditions. The high incidence of embryo death and reduced embryo weight at GD6–14 dosing compared to GD14–21 dosing suggest that embryos are more sensitive to the deleterious effects of HEPP than fetuses; however, the faster elimination observed at late gestation could also contribute to the lower toxicity observed during the fetal period. Because the maternal HEPP plasma levels and the AUC values were positively correlated with embryo/fetal toxicity end points, both pharmacokinetic parameters could be reliable indicators of offspring exposure and consequently of potential toxicity. These data suggest that the length of time that HEPP is present in the maternal plasma at a sufficiently high concentration could be determinant of adverse effects in the offspring.

Lack of interaction between HEPP, a new antiepileptic agent, and carbamazepine in rabbits

The effect of the combination of a new anticonvulsant drug HEPP and carbamazepine (CBZ) on the pharmacokinetics of HEPP and CBZ was investigated using rabbits as an animal model. The study was performed in 18 male New Zealand white rabbits which were randomly divided into three groups, according to a balanced incomplete block design of three treatments and two periods. Plasma concentrations for HEPP and CBZ were assayed using HPLC methods. The results showed that the pharmacokinetic parameters C(max), AUC and t(1/2) were not statistically different when HEPP was administered alone and with CBZ, (AUC(0-alpha) 82.86+/-19.40 vs 83.24+/-12.56 microg h ml(-1); t( 1 2 beta) 3.40+/-0.29 vs 3.36+/-0.45 h; C(max) 18.93+/-2.99 vs 19.79+/-2.68 microg ml(-1) and T(max) 1.27+/-0.16 vs 1.22+/-0.11 h for HEPP alone and HEPP plus CBZ respectively. Evaluation of the pharmacokinetic parameters of CBZ showed, AUC(0-inf) 61.5+/-21.7 vs 67.4+/-23.8 microg h ml(-1); t(12) 4.60+/-1.54 vs 4.41+/-1.35 h; C(max) 8.45+/-3.83 vs 8.70+/-2.59 microg ml(-1) when the drug was administered alone and CBZ plus HEPP, respectively. Our data indicate that there is no effect on the pharmacokinetics of either HEPP or CBZ, when they are administered simultaneously.

Pharmacokinetic interaction in rabbits between a new anticonvulsant, DL-3-hydroxy-3-ethyl-3-phenylpropionamide, and phenytoin

The effect of phenytoin on the disposition of DL-3-hydroxy-3-ethyl-3-phenylpropionamide (HEPP) has been studied in New Zealand white rabbits. Plasma HEPP levels decreased when the drug was administered with phenytoin. The area under the plasma concentration-time curve was reduced by 56.49% (from 43.23+/-7.0 to 18.81+/-2.03 microg h mL(-1)), the elimination half-life was also significantly (P<0.01) reduced (from 2.68+/-0.35 to 1.04+/-0.07 h) and the clearance was increased (from 0.35 to 0.81 L h(-1) kg(-1)). In-vitro protein binding to bovine serum albumin (BSA) and plasma was evaluated by equilibrium dialysis. Plasma protein binding was low (between 33.69 and 37.43% at concentrations ranging from 6.25 to 100 microg mL(-1)). The compound binds preferentially to albumin with an association constant (Ka) of 3.81 x 10(3) M(-1) at 37 degrees C. The results suggest a pharmacokinetic interaction between phenytoin and HEPP, probably on the drug-metabolizing enzyme system in the liver.